Today, in order to fulfill current emission legislation, more or less all vehicles with an Internal Combustion Engine (ICE) are provided with an exhaust gas aftertreatment device comprising some kind of catalytic converter.
The catalytic converter for reduction of exhaust gas emissions from an ICE generally consists of a tubular, longitudinal body with an inlet and an outlet, wherein the inlet is arranged on the exhaust side of the ICE, for receiving exhaust gas emissions from the ICE, and an outlet is arranged for discharging exhaust gas emissions treated in the catalytic converter. The inlet is in flow communication with the outlet. Additionally, the catalytic converter generally comprises at least one catalytic converter substrate arranged between the inlet and the outlet of the catalytic converter. A catalytic converter substrate generally comprises a channeled structure which the exhaust gases can pass through while being exposed to the large surface area of the catalytic converter. For petrol engines the most frequently used catalytic converter substrate is generally Three Way Catalyst (TWC), while Diesel Oxidation Catalyst (DOC) and/or Lean NOx Trap (LNT) generally are most frequently used for diesel engines. It is also preferred that the TWC or the DOC/LNT is supplemented by a substrate with selective catalytic reduction (SCR) functionality for improved NOx reduction. The underlying mechanisms and the selection of catalytic converter are not part of the disclosure per se and is not further discussed herein.
However, using more than one catalytic converter substrate can be problematic since catalytic converters often are associated with design restrains due to the limited available space in the engine compartment of passenger cars. Small catalytic converters are preferred from an engine packaging perspective, but small catalytic converters usually means that the flow distance between the inlet and the catalytic converter substrates of the catalytic converter is limited. Limited distance means that the time and distance during which mixing of the exhaust gas emissions can occur is limited. Insufficient mixing of the exhaust gas emissions gives inhomogeneous exhaust gas emission mixture. This might e.g., be problematic for emission gas sensors, arranged in the exhaust gas emission flow, to work properly and give accurate emission measurements.
Other problematic areas for catalytic converters are high back pressure and insufficient heating. Heating of the catalytic converter is crucial since the catalytic converter is most effective at relatively high temperatures. Thus, it is desirable that catalytic converter reaches its optimum operation temperatures as soon as possible. However, at the same time high temperatures, and big fluctuations in temperature, are stressful for the components of the catalytic converter. Different approaches are used in order for the catalytic converter to reach desired operation temperature as quickly as possible, e.g., the combustion and fuel injection of the engine may be controlled for generating additional heat or the catalytic converter may be arranged as close to the engine exhaust gas emissions outlet as possible, where the exhaust gas emissions are warmest.
Insufficient mixing of the exhaust gas emissions are of particular interest if a substrate with SCR functionality is used. For substrates with SCR functionality, a liquid or gaseous reductant is introduced in the exhaust gas emission flow in order for the reductant and exhaust gas emissions to mix before the substrate with SCR functionality. Consequently, sufficient mixing is essential for the substrate with SCR functionality to work properly.
US 2012/0110989, herein considered to be incorporated by reference, discloses an exhaust-gas aftertreatment device for an internal combustion engine, wherein the device comprises a catalytic converter comprising a tubular member, a pipe member, one catalytic converter substrate and a deflector means. By utilizing the pipe member and the deflector means, the catalytic converter arrangement according to US 2012/0110989 provides prolonged mixing period before the single catalytic converter for improved efficiency. Also, the pipe member and the deflector means are configured to reduce the amount of emissions in liquid form before the exhaust gas emissions reaches the single catalytic converter by using heat transferred from the exhaust gas emissions to the pipe member and the deflector means. This effect is additionally promoted by arranging a layer of porous material between the downstream side of the pipe member and the deflector means.
However, there is still a need for further improvements.